China Eastern 737-800 MU5735 accident March 2022
Only half a speed-brake
As a general question, how reliable is Chinese accident investigation and reporting?
One of the power-pillars of a controlling government, anywhere, is providing (a sense of) security to its own people. Falling aeroplanes are cross with the marketed purpose.
On top of that, as W.C.'s far eastern twin would have said: "Never let a good uproar go to pass without public punishment."
Only half a speed-brake
Firewalling the thrust levers from stable cruise will have a marked pitch-up but nowhere near what's required to cause an upset. At FL290 the engines operate near maximum available thrust for thermodynamic and engineering efficiency anyway.
The second part, overzealous pushover and nosedive, might be similar. But the trigger needs to be a different one.
As well, noted by wiggy earlier, the geometry of TLs in their forward cruise position places the TO/GA buttons out of the way, not to mention those are completely different designs between 767 and 737. Or someone reaching for the flap lever at that altitude...
I linked the accident report only for completeness, the dynamics look uncorrelated IMHO.
The second part, overzealous pushover and nosedive, might be similar. But the trigger needs to be a different one.
As well, noted by wiggy earlier, the geometry of TLs in their forward cruise position places the TO/GA buttons out of the way, not to mention those are completely different designs between 767 and 737. Or someone reaching for the flap lever at that altitude...
I linked the accident report only for completeness, the dynamics look uncorrelated IMHO.
Last edited by FlightDetent; 22nd Mar 2022 at 18:54.
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[in reply to a questions about Chinese accident investigation quality]
I agree. Also keep in mind that under ICAO rules they are required to allow representatives from the country of aircraft design (USA) and aircraft manufacturer (also USA) to participate in the investigation:
They won't have a say in the report, but will be allowed to observe, and can write their own additional, if unofficial, reports.
Traditionally, the engine design and manufacturing companies also request and receive permission to send representatives, but there is no such obligation under ICAO Annex 13.
5.18 The State of Registry, the State of the Operator, the State of Design and the State of Manufacture shall each be entitled to appoint an accredited representative to participate in the investigation.
Traditionally, the engine design and manufacturing companies also request and receive permission to send representatives, but there is no such obligation under ICAO Annex 13.
The video from this still is real. The guy in the video speaks Cantonese with a really heavy accent and the two words I understood was "直落" which means "straight down." There are two provinces in the whole of China (besides HK and Macau) where locals speak Cantonese.. Guangxi (where the plane went down) and Guangdong.
Too many armchair experts in this thread
Too many armchair experts in this thread
If the video was taken perpendicular to the flight path, then that would be correct.
If it was taken parallel to the flight path, it might not have been able to pick up a horizontal component of the plane going away from the video camera.
Either way, it shows a high rate of descent.
I’ll leave it to others to map out where the camera was relative to the flight path and won’t post again on this thread.
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I have not seen anything relating to ATC chatter anywhere. I have no experience with Chinese ATC. Is it something that we are likely to see released, or will it fall into the CCP information void?
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(Not a professional, just somebody following the news, so my terminology is off.) The latest news from today is that they entered the air control zone of Guangzhou not long before the crash. The ATC noticed that they started a steep dive and repeatedly tried to reach them, but got no reply whatsoever until the end.
If we are to believe the FR24 data, it does not logically back up a trim runaway scenario. The speed (I'm still unsure whether we are talking G/S or TAS), drops slightly just before descent. This would not be abnormal if this was TOD as the aircraft sequences to ECON descent speeds (Mach). But then at about the time the descent rate increases exponentially, the speed is shown as a good 70-90Kts less than Cruise/TOD schedule. This anomaly lends itself to some other form of event unless the data table has a high inaccuracy capability. Only the CVR/FDR will allow those that analyze these events the opportunity to piece together the possible causes, hopefully arriving on a conclusive reason.
Your assumption about a decreasing "speed" in the FR24 data, happening before the upset is wrong. Only once the upset starts, the Ground Speed goes down, understandable, since the airplane is diving with more 20K ft/min. So no anomaly in the reported FR24 speeds.
You understand that yoke trim switches have an "power button" button and a "direction" button? It's unlikely both switches would fail. Also, faulty yoke switch inputs can be immediately overridden by pulling/pushing on the stick in the opposite direction, then the cutout switches can be used.
Avionics maintenance engineer (40 years)
Avionics maintenance engineer (40 years)
Of course, the trim switches are as you describe, though that does not imply, a trim-runaway is impossible. Hence, the presence of the double trim cut-off switches. These are there, because these are regulatory and technically needed.
I keep coming back to the (speculated and in no way confirmed) fact that they were TOD.
TOD in the 738 is fairly benign;
A few buttons punched on the FMC- VNAV Checked, etc and on the MCP- ALT put in (and depending on whether it was VNAV or only LNAV - V/S - can you really go sooo wrong doing any of that? Other FMC Inputs at that time pertain to Flap select for Landing, etc - nothing to do with anything directly connected to changing the physical config of the aircraft at that time.
and the Checklist is only;
Pressurization
Recall
Autobrake
Landing Data
Approach Briefing
So there's nothing mechanical there that moves anything physical on the airframe. (Apart from Autobrake dial on the MIP)
It's so wierd - TOD is like the last phase of flight where something suddenly goes so completely wrong. The only thing you can do on the MCP (and that's the only thing you actually touch apart from selecting your Autobrake setting on the MIP) at TOD to crash the aircraft is dial in ALT 0 and V/S 8000/FPM. That will get you spat out. But to do that the bloke sitting next to you - checking your work - would have something to say about it. And if it was me - I'd challenge you as to why you'd dialled in those Extreme MCP ALTS and V/S and if you wearn't making sense I'd probably knock you out and have you removed from the cockpit.
It doesn't make sense - it just fell out of the sodding sky. For me that makes it Mech Fail. Something went 'Twang' and it became unrecoverable (with the best will in the World being flown up front) but I have absolutely no idea how or why. But I am very anxious to know.
RIP
TOD in the 738 is fairly benign;
A few buttons punched on the FMC- VNAV Checked, etc and on the MCP- ALT put in (and depending on whether it was VNAV or only LNAV - V/S - can you really go sooo wrong doing any of that? Other FMC Inputs at that time pertain to Flap select for Landing, etc - nothing to do with anything directly connected to changing the physical config of the aircraft at that time.
and the Checklist is only;
Pressurization
Recall
Autobrake
Landing Data
Approach Briefing
So there's nothing mechanical there that moves anything physical on the airframe. (Apart from Autobrake dial on the MIP)
It's so wierd - TOD is like the last phase of flight where something suddenly goes so completely wrong. The only thing you can do on the MCP (and that's the only thing you actually touch apart from selecting your Autobrake setting on the MIP) at TOD to crash the aircraft is dial in ALT 0 and V/S 8000/FPM. That will get you spat out. But to do that the bloke sitting next to you - checking your work - would have something to say about it. And if it was me - I'd challenge you as to why you'd dialled in those Extreme MCP ALTS and V/S and if you wearn't making sense I'd probably knock you out and have you removed from the cockpit.
It doesn't make sense - it just fell out of the sodding sky. For me that makes it Mech Fail. Something went 'Twang' and it became unrecoverable (with the best will in the World being flown up front) but I have absolutely no idea how or why. But I am very anxious to know.
RIP
Last edited by Auxtank; 22nd Mar 2022 at 23:36.
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[in reply to a questions about Chinese accident investigation quality]
I agree. Also keep in mind that under ICAO rules they are required to allow representatives from the country of aircraft design (USA) and aircraft manufacturer (also USA) to participate in the investigation:
They won't have a say in the report, but will be allowed to observe, and can write their own additional, if unofficial, reports. Traditionally, the engine design and manufacturing companies also request and receive permission to send representatives, but there is no such obligation under ICAO Annex 13.
I agree. Also keep in mind that under ICAO rules they are required to allow representatives from the country of aircraft design (USA) and aircraft manufacturer (also USA) to participate in the investigation:
They won't have a say in the report, but will be allowed to observe, and can write their own additional, if unofficial, reports. Traditionally, the engine design and manufacturing companies also request and receive permission to send representatives, but there is no such obligation under ICAO Annex 13.
The profile plot from post #52 is interesting as it does not show a "vertical" drop, probably more likely between 30-40 deg trajectory. I also agree with a post that highlighted the two ADSB blips where there is an extended gap between responses of say 15 seconds, where both steep descents seem to originate, was there some sort of electrical fault or factor? From both ADSB cutouts the aircraft initiates a steep descent and lurches left, from what the plot shows. After the first there seems to be a turn of sorts back to the right and some recovery action by 10,000 feet then a second gap in returns and it goes back into the final steeper profile.
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The recorders will almost certainly not be serviceable, i. e. they will be destroyed and will not work.
But the memory modules will almost certainly still be readable; they are in some of the toughest enclosures you can imagine, they can protect the memory from shock in excess of 1000 G acceleration, and prolonged hot fires. It is the enclosures' only job to protect the memory modules in precisely this kind of situation. This looks like a head-on crash with a velocity not too different from the Germanwings murder-suicide, so the entire aircraft acts as a crumple-zone reducing the acceleration experienced by the recorders.
The problem will be to find them. This can take weeks.
But the memory modules will almost certainly still be readable; they are in some of the toughest enclosures you can imagine, they can protect the memory from shock in excess of 1000 G acceleration, and prolonged hot fires. It is the enclosures' only job to protect the memory modules in precisely this kind of situation. This looks like a head-on crash with a velocity not too different from the Germanwings murder-suicide, so the entire aircraft acts as a crumple-zone reducing the acceleration experienced by the recorders.
The problem will be to find them. This can take weeks.
I keep coming back to the (speculated and in no way confirmed) fact that they were TOD.
TOD in the 738 is fairly benign;
A few buttons punched on the FMC- VNAV Checked, etc and on the MCP- ALT put in (and depending on whether it was VNAV or only LNAV - V/S - can you really go sooo wrong doing any of that? Other FMC Inputs at that time pertain to Flap select for Landing, etc - nothing to do with anything directly connected to changing the physical config of the aircraft at that time.
and the Checklist is only;
Pressurization
Recall
Autobrake
Landing Data
Approach Briefing
So there's nothing mechanical there that moves anything physical on the airframe. (Apart from Autobrake dial on the MIP)
It's so wierd - TOD is like the last phase of flight where something suddenly goes so completely wrong. The only thing you can do on the MCP (and that's the only thing you actually touch apart from selecting your Autobrake setting on the MIP) at TOD to crash the aircraft is dial in ALT 0 and V/S 8000/FPM. That will get you spat out. But to do that the bloke sitting next to you - checking your work - would have something to say about it. And if it was me - I'd challenge you as to why you'd dialled in those Extreme MCP ALTS and V/S and if you wearn't making sense I'd probably knock you out and have you removed from the cockpit.
It doesn't make sense - it just fell out of the sodding sky. For me that makes it Mech Fail. Something went 'Twang' and it became unrecoverable (with the best will in the World being flown up front) but I have absolutely no idea how or why.
RIP
TOD in the 738 is fairly benign;
A few buttons punched on the FMC- VNAV Checked, etc and on the MCP- ALT put in (and depending on whether it was VNAV or only LNAV - V/S - can you really go sooo wrong doing any of that? Other FMC Inputs at that time pertain to Flap select for Landing, etc - nothing to do with anything directly connected to changing the physical config of the aircraft at that time.
and the Checklist is only;
Pressurization
Recall
Autobrake
Landing Data
Approach Briefing
So there's nothing mechanical there that moves anything physical on the airframe. (Apart from Autobrake dial on the MIP)
It's so wierd - TOD is like the last phase of flight where something suddenly goes so completely wrong. The only thing you can do on the MCP (and that's the only thing you actually touch apart from selecting your Autobrake setting on the MIP) at TOD to crash the aircraft is dial in ALT 0 and V/S 8000/FPM. That will get you spat out. But to do that the bloke sitting next to you - checking your work - would have something to say about it. And if it was me - I'd challenge you as to why you'd dialled in those Extreme MCP ALTS and V/S and if you wearn't making sense I'd probably knock you out and have you removed from the cockpit.
It doesn't make sense - it just fell out of the sodding sky. For me that makes it Mech Fail. Something went 'Twang' and it became unrecoverable (with the best will in the World being flown up front) but I have absolutely no idea how or why.
RIP
I suspect it's chicken and egg speculation now, until the recorders are recovered and read:
How did the crew's actions at TOD contribute to this catastrophic event, or had something failed on the plane just prior to TOD
My thoughts are with the families of those lost
Retired B driver
My one flight on a chinese domestic airline was just over 25 years ago and it was a Boeing but cant recall the model. What I do recall is at TOD the autopilot was disengaged and close to full spoilers deployed. So it was a loud rough decent for us. Back then the flight crew were straight from the chinese airforrce and their level of English was basic. I am sure things have improved there since then. I am a retired CPL.
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Estimate speed
Someone with more video analysis skills than me could provide a rough speed calculation based on the video using the aircraft lenght as scale reference? Surely it won’t be 100% accurate but I think that the Ground Speed reported from FR24 data is far from accurate and is not even close to the TAS experienced in the final moments. With 3000ft/min a 738 can barely keep 300knots indicated. With 30.000fpm there is no way the speed was lower than 600kts especially with so much potential energy from FL300.
edit: if no such speed was ever reached than a recovery attempt should be realistic, and if a recovery was even partially successful that means that the initial upset was probably not as catastrophic as someone might expect.
edit: if no such speed was ever reached than a recovery attempt should be realistic, and if a recovery was even partially successful that means that the initial upset was probably not as catastrophic as someone might expect.
My one flight on a chinese domestic airline was just over 25 years ago and it was a Boeing but cant recall the model. What I do recall is at TOD the autopilot was disengaged and close to full spoilers deployed. So it was a loud rough decent for us. Back then the flight crew were straight from the chinese airforrce and their level of English was basic. I am sure things have improved there since then. I am a retired CPL.
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My one flight on a chinese domestic airline was just over 25 years ago and it was a Boeing but cant recall the model. What I do recall is at TOD the autopilot was disengaged and close to full spoilers deployed. So it was a loud rough decent for us. Back then the flight crew were straight from the chinese airforrce and their level of English was basic. I am sure things have improved there since then. I am a retired CPL.
